The field to which my invention relates is that generally denoted as electrical machining. Included in this field are electrical discharge machining, electrochemical machining and electrochemical discharge machining in which processes metal removal is accomplished by passing of discrete electrical impulses across a coolant filled gap. In electrical discharge machining, the coolant is a dielectric fluid such as kerosene or transformer oil. The process and apparatus of electrical discharge machining are explained and shown in my U.S. Pat. No. 3,054,931, issued Sept. 18, 1962 and entitled "Electric Power Supply Apparatus for Electric Discharge Machining." The process of electrochemical machining is explained and shown in my U.S. application Ser. No. 316,955, filed on Oct. 17, 1963 (now U.S. Pat. No. 3,357,912, issued Dec. 12, 1966) while that of electrochemical discharge machining is disclosed in my co-pending U.S. application Ser. No. 475,375, filed on July 28, 1965 .Iadd.(now U.S. Pat. No. 3,616,343).Iaddend.. In each of these electrical machining processes, an electrode servo feed system is employed to maintain an optimum gap spacing between electrode and workpiece. A liquid coolant in the form of a dielectric or electrolyte, depending on the process used, is circulated through the gap continuously during the machining operation. If the initial downfeed is made with too high a power pulse input to the gap, damage can be caused to workpiece, electrode or both. Provision is made by the present invention to provide for current reduction by concomitantly or separately increasing pulse off-time and decreasing pulse on-time during gap open circuit. When the gap becomes too narrow or is bridged or contaminated by eroded particles, an abnormal condition called "gap short circuit" can arise. My invention is effective in controlling all the foregoing types of electrical machining where a succession of power pulses is utilized and the variation in dimension and condition of the machining gap occurs from time to time. While the present invention is described in terms of transistor switch circuitry, my invention is not so limited, but is equally applicable to any electronic switch arrangement. By " electronc switch" I mean any electronic control device having three or more electrodes comprising at least two principal or power electrodes acting to control current flow in the power circuit, the conductivity between the principal electrodes being determined by a control electrode within the switch whereby the conductivity of the power circuit is regulated statically or electrically without movement of mechanical elements within the switch. Included within this definition are vacuum tubes and transistors in which turn-on is accomplished by a control voltage applied to the control electrode and in which turn-off is accomplished automatically in response to the removal of that control voltage. Also included in the definition are devices of the gate type in which turn-on is accomplished by a control voltage applied to the control electrode which control voltage may be then removed and in which turn-off is accomplished by application of a subsequent control voltage to the control electrode. An additional class of electronic switches called electronic trigger devices falls within this definition and includes ignitrons, thyratrons and semiconductor controlled rectifiers. By "electronic trigger device" I mean any electronic switch of the type which is triggered on at its control electrode by a pulse and is turned off by reverse voltage applied for a sufficient time across its principal electrodes.